Download - Rick PerleyEVLA Advisory Committee Meeting September 6-7, 2007 Some Illustrative Use Cases Rick Perley.

Rick Perley EVLA Advisory Committee MeetingSeptember 6-7, 2007

Some Illustrative Use Cases

Rick Perley


Science Use Cases

• We have begun careful consideration of science use cases, primarily to:– identify the primary correlator modes needed for early

science, and – identify the modes which will cover all the anticipated

science applications.

• I give a few examples to justify our belief that a very few correlator setups will cover an enormous range of early science.


Correlator Basics(3-bit Initial Quantization,

4-bit Re-Quantization)

• The correlator comprises four quadrants. Each processes all baselines, for all antennas, for one input baseband pair (BBP).

• Each BBP is subdivided into 16 sub-band pairs (SBP), with BW equal to any of 128, 64, 32, …, .03125 MHz.

• All 16 * 4 = 64 SBPs can be tuned independently to (almost) any frequency and BW.

• Each of the 64 SBPs provides 256 spectral channels, which can be divided amongst 1, 2, or 4 polarization products.

• The resources available to any SBP can be given to any other SBP to increase spectral resolution.

• Recirculation is available for any, and all, SBPs, to provide extra, higher spectral resolution.


Correlator Resource Allocation Matrix

• Each SBP (blue rectangle) provides 256 channels for one, two, or four polarizations (for IQ = 3, RQ = 4)• Each of the 64 SBPs has a separate, independent frequency and bandwidth.

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16 independent digital sub-bands


CRAM example:Resource Concatenation

• Concatenation has been implemented to provide more resources to the 17 individual SBP tunings (black dots).

• In addition, recirculation is available for all SBPs.


Example 1: Full Band Coverage

• This means covering the maximum bandwidth, for each band, with all Stokes combinations, with uniform frequency resolution.

• This setup would be used for – ‘continuum’ (maximum sensitivity) observations,

where very high spectral resolution is not needed. – spectral line surveys, for cases where the basic

correlator channelization is sufficient to detect spectral transitions.


Summary of Coverage(with 4-bit RQ)

BW v NchGHz kHz km/sec

L 1.024 31 6 131076S 2.048 125 12 65536C 4.096 500 25 32768X 4.096 500 16.5 32768U 6.144 2000/500 37/12 24576K 8.192 2000 27 16384A 8.192 2000 13 16384Q 8.192 2000 6 16384

The output consists of 64 full-polarization data streams.


Data Rate Comment

• The correlator has the capability of producing a large volume of data in short time.

• Roughly, the data rate is given by:

• With 1 second averaging, 16384 channels will produce data at a rate of 62 MByte/sec.

• For A-configuration, an averaging time of 2.5 seconds is adequate for full-beam imaging => 25 MB/sec.

• (Previous example provides sufficient spectral resolution for full-beam, full-band imaging for all frequencies and configs.

Byte/sec/)1(5~ sectNNND antantchan


High RFI Situations

• For L and S bands, we expect high RFI in some SBP. • For this case, there is a 7-bit RQ mode, which can be

turned on for individual SBPs. • The extra bit depth comes at a cost in spectral resolution:

– S-Band: Resolution of 500 kHz (50 km/sec) over full BW with (RR, LL) only, OR with full polarization over 1 GHz total bandwidth.

– L-Band: Resolution of 500 kHz (100 km/sec) over full BW with all polarizations, OR, 125 kHz (25 km/sec) with (RR,LL) only.

• Most likely, we will be able to use 4-bit RQ in most sub-bands.


Example 2: Multiple spectral lines.

• How many spectral lines can be simultaneously observed, with ~1km/sec. velocity resolution, and with full polarization?


64 Different Lines, with Full Polarization!

BW Nch v Vel.Cov. TotalMHz kHz km/s km/sec. Nchan

Q 32 256 125 .83 213 65536A 32 256 125 1.1 282 65536K 16 512 31 .41 210 131072U 16 512 31 .63 320 131072X 16 512 31 .94 480 131072C 8 1024 7.8 .39 400 262144S 8 1024 7.8 .78 320 262144L 4 2048 2.0 .39 800 524288


Variable Resolution for Each Transition

• It is important to note that *each* of the 64 spectral lines can be observed with a different spectral resolution.

• With full polarization, the available resolutions will be: 125, 31, 7.8, 2.0, … kHz.

• With fewer transitions covered, or (RR,LL) only, other resolutions can be obtained.


High RFI environment at L-band.

• At L-band, many SBPs may be in high RFI environments.

• As a worst case, suppose ALL sub-bands need 7-bit RQ. Then:– 16 lines can be tuned with full polarization with

0.4 km/sec resolution, OR– 32 lines can be tuned with (RR,LL)

polarization, and the same resolution.


Example 3: Continuum plus Targeted Spectral Lines

• Suppose an observer wants both the full continuum , and to be able to ‘target’ specific lines with ~1 km/sec spectral resolution.

• What are the possibilities?


For K, A, Q Bands

• In these bands, some continuum BW must be given up to obtain high-resolution spectral transitions. Some possibilities are:

1. 6 GHz of continuum, and 16 spectral lines, or2. 4 GHz of continuum, and 32 spectral lines, or3. 2 GHz of continuum, and 48 spectral lines.

– All of these with full polarization, and independently adjustable frequency and resolution for each line.

– The continuum is resolved at 2 MHz/channel, the lines at any of 500, 125, 31.2, 7.8, … kHz.

– This is not a practical example -- no zoom on the spectral lines within the reserved continuum bands.


C and X Bands

• In the 4-8, and 8-12 GHz bands, one would get:– Full 4 GHz BW continuum observed with 2 MHz channel

resolution in all four polarization products, giving a total of 8192 channels.

PLUS– 32 individual lines (of arbitrary frequency) observed with

512 channels/spectrum, full polarization, and frequency resolution of 31.2 kHz (1.56 km/sec at 6GHz)

• Total number of channels out = 67584. • With a 1-second integration time, the output data

rate is about 256 MB/sec.


Example Four: Claire’s Challenge!

Claire has proposed two K-band experiments:1. Studies of a Massive Star-Forming Region

– 32 molecular transitions, to be observed at 0.2 km/sec, and– 8 RRLs, to be observed with 1 km/sec.– Some reasonable amount of continuum.

2. Studies of a Cold Dark Cloud. – 54 molecular transitions (mostly heavy molecules) requiring

0.01 km/sec resolution.– Some reasonable amount of continuum

Can the EVLA do all this?


Massive star-forming region

• observe high-density tracers NH3, all available transitions from (1,1) to (8,8), and CH3OH; gives density and temperature structure of hot cores (very young, massive, protostars)

• observe shock tracers, interaction of protostars with surrounding cloud: transitions of SO2, H2O, OCS, H2CS, H2CO, OH

• observe radio recombination lines and continuum emission from a nearby HII region

• spectral resolution required for molecular lines: 0.2 km/s• spectral resolution required for RRLs: 1 km/s• need as much line-free continuum as possible for the free-

free emission


Cold dark cloud

• observe low-energy, long carbon-chain molecules and high-density tracers in a dark cloud to study pre-biotic chemistry: NH3, HNCO, C4H, C5H, C6H, C3N, CCS, CCCS, HCCCN, HCCNC, HNCCC, HC5N, HC7N, HC9N, H2C3, CH3CN, c-C3H2

• observe continuum to detect embedded protostars/disks/jets

• spectral resolution required for molecular lines: 0.01 km/s• need as much line-free continuum as possible for the

dust/ionized gas emission


Hydrogen recombination lines

H71

H70

H69

H68

H67

H66

H65

H64

H63

H62


Massive SFR

• Tune the four frequency pairs to:1. 18.6 – 20.6 GHz 3RRL + 1 Mol (12 SBP free)2. 20.6 – 22.6 GHz 2 RRL + 3 Mol (11 SBP free)3. 22.6 – 24.6 GHz 2 RRL + 14 Mol (all SBP used)4. 24.6 – 26.6 GHz 1 RRL + 14 Mol. (one SBP free)

• Set the 32 SBPs covering the molecules to a BW = 16 MHz, providing 1024 channels in both RR and LL.

• Set the 8 SBPs covering the RRLs to BW = 32 MHz, providing 512 channels in both RR and LL.

• This leaves 24 SBPs to cover the continuum (at 128 MHz BW each), or for other transitions.


The entire spectrum


Within One of the BBPs


Cold Dark Cloud

• In this experiment, there are a total of 51 transitions between 18 and 26 GHz

• Tunings:1. 18 – 20 GHz: 17 transitions (uses all 16 SBP)2. 20 – 22 GHz: 13 transitions (uses 12 SBP, leaving 4 free)3. 22 – 24 GHz 12 transitions (uses 12 SBP, leaving 4 free)4. 24 – 26 GHz 9 transitions ( 7 SBP free)

– The required resolution can be obtained with BW = 4 MHZ, providing 4096 channels in each of RR and LL.

– A total of 417792 channels are required for these lines.– 15 SBPs remain for continuum observations.


Tentative Conclusions

• The WIDAR correlator offers tremendous resources for science.

• Simple rules govern the allocation of resources.

• All challenging science cases have (so far) been easily accommodated.

• More tough experiments are eagerly sought!